The present invention relates to a display device for a microcomputer.
Conventionally, in order to drive a liquid crystal display (LCD) of m.times.n dots (m, n: natural numbers), the following components are required: a RAM for display; a ROM for a character generator; a changeover gate for changing, an output from the display RAM or the character generator ROM; a liquid crystal driving circuit for driving segment electrodes and common electrodes of the LCD; and a liquid crystal display controlling circuit for controlling the operating timings of the aforementioned RAM, ROM changeover gate, and liquid crystal driving circuit.
First, in the case of executing graphic display, if an arbitrary address of the display RAM is designated by the liquid crystal display controlling circuit in a state in which display data corresponding to the dots of the LCD is stored in the RAM, the display data read out from the designated address of the RAM is delivered to the liquid crystal driving circuit via the changeover gate, thereby effecting display on the LCD with respect to each dot.
In addition, in the case of executing character display, a predetermined character pattern is set in advance in the character generator ROM by means of a mask. Then, if an arbitrary address of the display RAM is designated by the liquid crystal display controlling circuit in a state in which a character code corresponding to the predetermined character pattern is stored in the RAM, the character code read out from the designated address of the RAM is converted to display data by the character generator ROM. Subsequently, the display data is delivered to the liquid crystal driving circuit via the changeover gate, thereby effecting character display on the LCD (see Japanese Patent Laid-Open No. 175893/1988).
In the above-described conventional art, a timing controlling circuit for controlling the operating timings of the display RAM, the character generator ROM, the changeover gate, and the liquid crystal driving circuit is incorporated in the liquid crystal display controlling circuit. Therefore, if a predetermined character pattern is set in the a character generator ROM by means of a mask so as to effect character display, the mask for the timing controlling circuit is conventionally changed in such a manner that a timing controlling signal corresponding to the set contents of the ROM is generated by the timing controlling circuit, i.e., in correspondence with the set contents of the ROM.
However, although the contents of character patterns stored in the character generator ROM are open to the user, the timing controlling circuit must be made to correspond to the ROM by changing the mask each time a new character font is set in the ROM. Accordingly, there have been drawbacks because the masks are expensive, a long time is required to produce a mask following a request of the user, and required for each mask. Consequently, the user is compelled to defray huge expenses due to increased development costs, while the developer is unable to speedily provide a device desired by the user.